Linear motion variable resistor



Oct. 21, 1958 M. E. BOURNS ET AL 2,857,497

LINEAR MOTION VARIABLE RESISTOR Filed April 30, 195:: 2 Sheets-Sheet 1 FIG. 4

INVENTORS MARLAN E. BOURNS EDWARD J. GOEPPINGER lo I If I BY AGENT M. E. BOURNS ET AL LINEAR MOTION VARIABLE RESISTOR Filed April 50, 1953 2 Sheets-Sheet 2 FIGLI 7 loll I047 |o 5 lO'O;

INVENTORS MARLAN E. BOURNS EDWARD J. GOEPPINGER AGE/v7 United States Patent LINEAR MOTION VARIABLE RESISTOR Marian E. Bourns and Edward J. Goeppinger, Riverside, Califi; said Goeppinger assignor to said Bourns Application April 30, 1953, Serial No. 352,215

6 Claims. (Cl. 201-62) The present invention relates to variable resistors or Potentiometers, and more particularly to that type of instrument wherein a contact-carrying member is moved along the length of a resistance element by rectilinear or reciprocating movement of an operating rod.

Heretofore, linear motion resistors have usually been made with the contact-carrying slider fixedly mounted on one end of a reciprocating operating rod, and the latter has been slidably supported on the instrument housing for longitudinal movement. The other end of the rod projects from the housing and is attached to a movable actuating member on the device with which the resistor is associated. Movement of the said actuating member causes the contact-carrying slider to be shifted along the length of the resistance element.

One of the serious disadvantages of this arrangement lies in the fact that the instrument must be precisely aligned with the actuating member of the associated device; otherwise, misalignment will cause bending of the operating rod or binding of the instrument, or will cause excessive wear of the operating rod bearing in the instrument, or of the device actuating the instrument. The misalignment problem in conventional linear motion resistors, as heretofore constructed, is further magnified by the fact that the contact-carrying member is rigidly fixed to the operating rod, and therefore any deflection or bending of the rod under side thrust results in displacement of the contact toward or away from the resistance element. The consequence of this is that the contact bears harder against the resistance element at one end thereof than at the other. The increased pressure at the one end causes increased wear of the contact and element, while the decreased pressure at the other end of the element tends to make the instrument more susceptible to vibrational error.

The primary object of the present invention, therefore, is to provide a linear motion variable resistor wherein the contact-carrying slider is accurately guided along a path parallel to the resistance element by a guide means on the housing entirely independent of the operating member, and the latter is connected to the slider by means providing for a limited amount of relative movement of the operator with respect to the slider to accommodate misalignment between the actuating member and the operator. The principal advantage of this arrangement is that it eliminates the problem of maintaining parallelism and alignment between the operating member and the slider, and insures accurate alignment and uniform pressure of the contact with respect to the resistance element at all times.

Another object of the invention is to provide a variable resistor of the class described, wherein the operating member is connected to the slider by means providing for a limited amount of relative movement by the operator with respect to the slider, so as to accommodate lateral displacement of one with respect to the other. This eliminates side thrust of the operating rod against its bearing, and prevents excessive bearing wear, binding,

and abnormal wear of the contact and resistance element.

A further object of the invention is to provide a linear motion variable resistor wherein the cooperating guide means on the housing and slider may readily be manufactured to such close tolerances and perfection of fit that vibration of the slider with respect to the resistance element is substantially eliminated, thereby eliminating hash or noise. Hash, or noise, may be defined as electrical fluctuations in resistor output resulting from intermittent electrical discontinuities between the contact and the resistance element, and is a serious problem with linear motion resistors of conventional design owing to the fact that it is practically impossible to make the operating rod and its bearing with such close tolerances and perfection of fit that the rod will not vibrate within the bearing under conditions encountered in aircraft and missile use. Such vibration of the operating rod causes the contact assembly, which is attached thereto, to chatter on the resistance element and thereby produce the electrical discontinuities referred to. Accuracy and precision of guiding the slider are further enhanced in the present invention by slidably supporting the slider immediately adjacent the point of contact with the resistance element. In prior resistors, the housing slidably supports the operating rod, and there is sometimes a considerable overhang of the rod and attached contact beyond the point of support.

Another object is to provide a linear motion resistor wherein the connection between the actuating member and the slider is flexible enough to accommodate misalignment, yet at the same time free from any backlash. In certain other conventional resistors of the linear motion type, the operating member takes the form of a pin projecting laterally from the slider through a slot in the housing. This arrangement has the advantage over the previously described construction of being more compact and less troublesome from the standpoint of alignment, although much trouble has been experienced with backlash between the side actuating pin and the device with which it is attached. A more specific object is to provide a resistor of the side actuating pin type, wherein the end of the pin is shaped to seat within a groove or socket in the actuating member and is split to engage the sides of the said groove or socket with a resilient spring pressure that serves to take up any clearance and eliminates backlash.

Still a further object of the invention is to provide a construction such that the mass of the contact-carrying slider can be reduced to the minimum, thereby minimizing inertia for better response, and also minimizing the effect of acceleration.

The foregoing and other objects and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following description of certain preferred embodiments thereof, reference being had to the accompanying drawings, wherein:

Figure 1 is a vertical sectional view through a linear motion resistor embodying the principles of our invention, taken at 1-1 in Figure 2;

Figure 2 is a transverse vertical section through the same instrument, taken at 2-2 in- Figure 1;

Figure 3 is a perspective view of the base member of the instrument;

Figure 4 is a fragmentary sectional view through a modified form of the invention;

Figure 5 is a vertical section through another embodiment of the invention, taken at 5-5 in Figure 6;

- Figure 6 is a transverse vertical section of the same, taken at 66 in Figure 5;

other form of the invention;

Figure 8 is a transverse vertical section through still another form of the invention.

Referring first to Figures 1 to 3 of the drawings, we have designated the instrument in its entirety with the reference numeral 10.. The instrument is seen to comprise a housing 11, which includes a base member 12, with ends 13 and 14, which are enclosed within a tubular sleeve or casing 15. The ends 13, 14 have circumferential grooves 16 formed therein, and seated within these grooves are rings 17, which seal the clearances between the ends and the casing 15. The casing is secured to the ends by screws 18.

The base member 12 is preferably formed of a thermosetting dielectric plastic material, such as phenolic resin, which may be molded, extruded, or machined to the form shown. In cross-section, the member 12 has the shape of a segment of a circle; the underneath surface of the member being cylindrically curved, and the top surface being flat. Two laterally spaced, parallel grooves 20 and 21 are formed in the flat, top surface of the member 12, and seated within these grroove are a collector strip 22 and wire-wound resistance element 23, respectively. Three angularly spaced locating holes or cavities 24 are drilled or otherwise formed in the ends of the member 12, and these are engaged by projections 25 extending inwardly from the faces of the end members 13, 14. This arrangement permits the base member 12 and end members 13, 14 to be assembled in accurately located relationship.

Mounted in and extending between the ends 13, 14 are two laterally spaced guide rods 26, which are parallel to the electrical members 22, 23. Slidably supported on the guide rods 26 is a contact-carrying slider 30. The slider 30 may be formed, as shown in Figure 2, with outwardly facing grooves or channels 31 formed in opposite sides thereof, which receive the guide rods 26. A flat plate 32 of dielectric plastic material is mounted on the bottom side of the slider 30, and attached to the plate is a U-shaped contact member 33, the ends of which wipe on the collector strip 22 and resistance element 23. The electrical signal is as picked up from the resistance element 23 and transferred over tothe collector strip 22 by the contact member 33, and the latter is insulated from the slider 30 by the dielectric plate 32.

Mounted in the left-hand end member 13 are three angularly spaced connector pin 34, which are adapted to receive a connector plug. Two of the pins 34 are connected to opposite ends of the resistance element 23; while the third pin 34 is connected to the collector strip 22. By this means, a voltage difference may be applied to the ends of the resistance element, and the voltage at any intermediate point engaged by the contact 33 will be transferred to the third pin.

The slider 30 is accurately guided along a path parallel to the electrical elements 22, 23 by the guide rods 26. The slider 30 i moved along the length of the elements 22, 23 by means of an operating member 35, which, in Figures 1 to 3, comprises a flexible wire. One end of the wire 35 is inserted into a hole in the end of the slider 30 and is secured therein by a set screw 36.

The wire 35 passes through a hole in the right-hand end member 14, which is sealed against the entrance of dirt by an O ring 41. The 0 ring 41 is seated within a counterbore 42, and is backed up by a tubular retainer 43. The other end of the wire 35 is attached to the movable actuating member (not shown) on the device with which the instrument is associated, and movement of the said actuated member is transmitted to the slider 30 to produce an electrical signal.

The operating member 35, being a flexible wire, provides a flexible connection between the actuating member and the slider 30 which eliminates any problem of misalignment between the two parts. If the instrument 10 should be misaligned with respect to the actuating member on the associated device, any non-parallelism in the travel of the actuating member and slider 30 is compensated for by the resilient operating member 35.

In the embodiment shown in Figure 4, the instrument is designated by the reference numeral 10', and is seen to be generally similar to the construction just described. In this form, however, the operating member 35' is seen to comprise a cylindrical rod, one end of which is reduced in diameter at 45 and extends through a hole 46 in slider 30'. The hole 46 is somewhat larger than the reduced portion 45, so that there is a substantial amount of clearance between them. A hole 50 is bored into the end of the slider 30, leaving a relatively thin wall 51, through which the hole 46 extends. By thus reducing the length of the hole 46, a substantial amount of loosenes can be obtained between the operating rod 35' and the slider 30. Wavy spring Washers 52 and 53 are interposed between the operating rod 35 and the opposite sides of wall portion 51. Spring washer 52 bears against the right-hand side of wall portion 51, and seats against a shoulder 54 at the junction of the reduced neck 45 with the main body of the rod 35. Spring washer 53 bears against the left-hand side of the wall portion 51, and seats against a regular flat washer 55, which is fastened to the reduced neck 45 in any suitable manner. The spring washers 52, 53 permit a limited amount of angular deflection of the rod 35 with respect to the slider 30, yet at the same time, take up all clearance so that there is no backlash between them. The connection between the operating rod 35 and the slider 30' is, in effect, a universal joint, permitting angular deflection of the rod with respect to the slider.

In the embodiment shown in Figures 5 and 6, the in strument is designated by the reference numeral 60, and is seen to comprise a generally rectangular, box-like housing made up of side walls 61 and 62, bottom wall 63, lid 64, and ends 65, 66. The collector strip 70 and wire-wound resistance element 71 seated within two laterally spaced, longitudinally extending grooves formed in the inside surface of the lid 64. The slider 72 is slidably supported on two laterally spaced guide rods 73, which are supported at their ends in partition members 74. An insulating plate 75 is attached to the top surface of the slider 72, and mounted on the plate is the contact member 76, which wipes on the elements 70, 71. The opposite ends of the resistance element 71 are connected to the terminals and 81, while the collector strip 70 is connected to a third terminal 82.

Projecting from the opposite side of the slider 72 is an operating pin 83, which projects through a slot 84 in the bottom plate 63. The pin 83 also extends througth a hole 85 and a flexible dust shield strip 86, and through a slot 87 in a cover plate 90, which is mounted against the underneath side of the bottom wall 63.

The dust shield strip 86 is slidably disposed within a shallow, longitudinally extending channel 91 formed in the underneath side of the bottom member 63. The ends of the dust shield strip 86 project into compartments 92 and 93, which are defined between the partition members 74 and ends 65, 66, respectively, and in these compartments, the strip coils up as hown in Figure 5. The strip 86 is preferably formed of spring material, and is formed to be self-coiling. Thus, as the pin 83 moves along the slots 84, 87, the slot openings are closed by the strip 86, which is pulled along With the pin. In this way, the interior of the holsing is sealed against the entrance of dirt or moisture, to protect the electrical elements.

The projecting outer end of the pin 83 is spherically shaped, as at 94, or otherwise rounded off, and is split diametrically at 95. The split is in the plane perpendicular to the line of travel of the pin 83, giving a degree of resiliency or compressibility in the direction of travel.

The spherical end 94 of the pin is seated within a groove 96 which is formed in an operating rod 97, the said operating rod extending generally parallel to the line of travel of the pin 83 and being attached at its other end to the actuating member of the device with which the instrument is associated. The groove 96 is slightly smaller than the diameter of the spherical end portion 94 of the pin, with the result that the pin is compressed slightly by insertion into the groove. The rounded end of the pin, seated within the groove 96, is thus the equivalent of a ball and socket joint, affording a limited amount of angular deflection of the rod 97 with respect to the pin 83. At the same time, the resiliency afforded by the split 95 takes up any clearances between the pin and the walls of the groove 96, thereby eliminating any backlash. As in the previously described embodiment, the slider 72 is thus guided along the path parallel to the electrical element 70, 71 by guide rods 73, while being moved along the said guide rods by an operating rod 97 which is entirely independent of the guiding function. Travel of the slider 72 is limited by retaining rings 98, which are seated within slots in the guide rods 73.

The embodiment shown in Figure 7 is another form of the invention, wherein the slider is guided and supported on ribs projecting inwardly from the side walls of the housing. In this case, the instrument 100 comprises a box-like housing, made up of a lid 101, side walls 102, and bottom plate 103. The collector strip 104 and resistance element 105 are seated within grooves in the lid 101, while the U-shaped contact member 106 is carried by a slider 107. Longitudinally extending ribs 110 project inwardly from the sides 102, and are engaged by grooves or channels formed in opposite sides of the slider 107.

The slider 107 is preferably formed in two parts, 111 and 112, which are drawn together and joined as one by rivets 113. An operating member in the form of a wire 114 sandwiched between the two halves 111, 112.

The advantage of this construction is that it eliminates the guide rods of the previous embodiments, while at the same time retaining the use of guiding means on the housing to support and guide the slider along a path parallel to the resistance element and collector strip. Since the sides 102 can be formed with extremely close tolerances of dimension and parallelism, it is possible to secure extremely accurate alignment of the slider with respect to the electrical elements. The flexible operating member 114 accommodates any misalignment between the instrument and the actuating part of the device with which the instrument is associated.

Figure 8 shows still another form of the invention, wherein the slider is supported and guided within grooves formed in the sides of the housing. In this case, the instrument 120 comprises a lid 121, sides 122, and bottom 123. The collector strip 124 and resistance element 125 are seated within slots in the lid 121, and the contact member 126 is carried on a slider 127. Longitudinally extending V-shaped channels 130 are formed in the sides 122, and these are engaged by correspondingly shaped wedge-like ribs 131 projecting from opposite sides of the slider 127. An operating member in the form of a wire 132 is connected to the slider 127 in any suitable manner. As in the case of the embodiment of Figure 7, the slider 127 is guided directly from the side walls of housing, eliminating the guide rods.

In each of the several embodiments of the invention described, the contact-carrying slider is accurately guided along a path parallel to the resistance element and collector strip by guide means on the housing independent of the operating means. At the same time, the operating member is connected to the slider by a flexible form of connection which accommodates any misalignment between the instrument and the device with which it is associated.

While We have shown and described in considerable detail what we believe to be the preferred forms of our invention, it will be understood that various changes may be made without departing from the scope of the broad claims appended hereto.

We claim:

l. A variable resistor comprising a housing, a rectilinear resistance element mounted on said housing, a slider having a contact mounted thereon engaging said -resistance element, a pair of parallel guide rods mounted on said housing parallel to said resistance element, said slider being slidably supported on said guide rods and prevented thereby from turning, a pin projecting laterally from said slider, an operating member movable in a direction generally parallel to the path of said slider, and means providing a flexible connection between the outer end of said pin and one end of said operating member, whereby the operating member is permitted a limited amount of angular movement with respect to said pin.

2. A variable resistor comprising a housing, a rectilinear resistance element mounted on said housing, a slider having a contact mounted thereon engaging said resistance element, means on said housing supporting and guiding said slider along a path parallel to said resistance element, a pin projecting laterally from said slider, the end of said pin being slotted diametrically in the plane perpendicular to the line of travel of said slider, and an operating member movable in a direction generally parallel to the path of said slider, said member having a cavity provided therein to receive the slotted end of said pin, the width of said cavity being such that said slotted end of said pin is slightly compressed thereby.

3. A variable resistor comprising a housing, a rectilinear resistance element mounted on said housing, a slider having a contact mounted thereon engaging said resistance element, a pair of parallel guide rods mounted on said housing parallel to said resistance element, said slider being slidably supported on said guide rods and prevented thereby from turning, a pin projecting laterally from said slider, an operating rod disposed generally parallel to the line of travel of said slider, and having a cavity provided therein, the end of said pin being slotted diametrically in the plane perpendicular to the line of travel of said slider, and said slotted end being disposed within said cavity,'the width of said cavity being such that said slotted end of said pin is slightly compressed thereby.

4. A variable resistor comprising a housing, a rectilinear resistance element mounted on said housing, a slider having a contact mounted thereon engaging said resistance element, a pair of parallel guide rods mounted on said housing parallel to said resistance element, said slider being slidably supported on said guide rods and prevented thereby from turning, a pin projecting laterally from said slider, the outer end of said pin being spherically formed and having a diametrical slot provided therein, an operating member disposed generally parallel to the line of travel of said slider and having a groove formed therein to receive said spherically shaped and slotted pin end, the width of said groove being such that said slotted pin end is slightly compressed.

5. A variable resistor comprising an elongated, generally rectangular, box-shaped housing, a lengthwise extending rectilinear resistance element mounted within said housing on one wall thereof, a pair of parallel guide rods mounted within said housing parallel to said resistance element, a slider slidably mounted on said guide rods and prevented thereby from turning, a contact mounted on said slider and engaging said resistance element, a pin projecting laterally from said slider, said housing having a lengthwise-extending slot formed in one wall thereof through which said pin projects, the outer end of said pin being rounded and slotted diametrically in a plane substantially perpendicular to the line of travel of said slider, said rounded and slotted end of said pin being adapted to be received within a grooved operating 4 member traveling generally parallel to the line of travel of said pin.

6. A variable resistor comprising a housing, a resistance element mounted on said housing, a linearly movable carrier having a contact thereon engaging said resistance element, means on said housing supporting and guiding said carrier along a path parallel to said resistance element, a pin projecting laterally from said carrier, an operating member movable in a direction generally parallel to the path of said carrier, and means providing a flexible connection between the outer end of said pin and said operating member, whereby the operating member is permitted a limited amount of movement with respect to said pin.

References Cited in the file of this patent UNITED STATES PATENTS Fanning June 16, Stevens June 5, Cameron Apr. 17, Oliphant Apr. 23, Kennedy Oct. 11, Batcheller Dec. 22, Wilson Jan. 18, Bourns July 18, Beatty June 24, 

